A unidirectional turbine is a turbine capable of providing unidirectional rotation from bidirectional or reversible fluid flow, such as in tidal estuaries or from shifting wind directions. Generally, three basic types of unidirectional reaction turbines are known, the Wells turbine, the McCormick turbine, and the Darrieus turbine.
The Wells reaction turbine is a propeller-type turbine that comprises a series of rectangular airfoil-shaped blades arranged concentrically to extend from a rotatable shaft, as shown in FIG. 1. Typically, the turbine is mounted within a channel that directs the fluid flow linearly along the axis of the rotatable shaft. The blades are mounted to extend radially from the rotatable shaft and rotate in a plane perpendicular to the direction of fluid flow. Regardless of the direction in which the fluid flows, the blades rotate in the direction of the leading edge of the airfoils, which, in FIG. 1, is counterclockwise.
The Wells turbine is capable of rapid rotation. The outer ends of its blades move substantially faster than the flowing air, causing high noise. Also, its efficiency is relatively low, because the effective surface area of the airfoil-shaped blades is limited to the outer tips, where the linear velocity is greatest. The blades cannot capture a substantial amount of the available energy in the fluid flowing closer to the shaft.
The McCormick turbine comprises a series of V-shaped rotor blades mounted concentrically between two series of stator blades, as shown in FIG. 2. The rotor blades are mounted for rotation in a plane perpendicular to the direction of fluid flow. The stator blades direct fluid flow to the rotor blades. To achieve unidirectional rotation with bidirectional fluid flow, the outer stator blades are open to fluid flowing from one direction, while the inner stator blades are open to fluid flowing from the opposite direction.
The McCormick turbine is more quiet and could be more efficient than the Wells turbine. However, its rotational speed is too slow for direct operation of an electric generator. Its configuration is also complex and expensive to manufacture.
The Darrieus machine is a reaction turbine with straight airfoil-shaped blades oriented transversely to the fluid flow and parallel to the axis of rotation, as shown in FIG. 3. The blades may be attached to the axis by circumferential end plates, struts, or by other known means. In some variations, the blades are curved to attach to the ends of the axis. A Darrieus reaction turbine having straight rectangular blades, mounted vertically or horizontally in a rectangular channel, has been placed directly in a flowing body of water to harness hydropower. The Darrieus turbine rotates with a strong pulsation due to accelerations of its blades passing through the higher pressure zones in the fluid that lowers the efficiency of the turbine.
Thus, a need still exists for a quiet, efficient, uniformly rotational, simple, unidirectional turbine that can operate at high speeds.